Håkelien Anne-Mari, Delbarre Erwan, Gaustad Kristine G, Buendia Brigitte, Collas Philippe
Institute of Basic Medical Sciences, Department of Biochemistry, Faculty of Medicine, University of Oslo, PO Box 1112 Blindern, 0317 Oslo, Norway.
Exp Cell Res. 2008 May 1;314(8):1869-80. doi: 10.1016/j.yexcr.2008.02.018. Epub 2008 Mar 7.
Autosomal dominant Emery-Dreifuss muscular dystrophy (EDMD) is characterized by muscle wasting and is caused by mutations in the LMNA gene encoding A-type lamins. Overexpression of the EDMD lamin A R453W mutation in C2C12 myoblasts impairs myogenic differentiation. We show here the influence of stable expression of the R453W and of the Dunnigan-type partial lipodystrophy R482W mutation of lamin A in C2C12 cells on transcription and epigenetic regulation of the myogenin (Myog) gene and on global chromatin organization. Expression of R453W-, but not R482W-lamin A, impairs activation of Myog and maintains a repressive chromatin state on the Myog promoter upon induction of differentiation, marked by H3 lysine (K) 9 dimethylation and failure to hypertrimethylate H3K4. Cells expressing WT-LaA also fail to hypertrimethylate H3K4. No defect occurs at the level of Myog promoter DNA methylation in any of the clones. Expression of R453W-lamin A and to a lesser extent R482W-lamin A in undifferentiated C2C12 cells redistributes H3K9me3 from pericentric heterochromatin. R453W-lamin A also elicits a redistribution of H3K27me3 from inactive X (Xi) and partial decondensation of Xi, but maintains Xist expression and coating of Xi, indicating that Xi remains inactivated. Our results argue that gene-specific and genome-wide chromatin rearrangements may constitute a molecular basis for laminopathies.
常染色体显性遗传性埃默里 - 德赖富斯肌营养不良症（EDMD）的特征是肌肉萎缩，由编码A型核纤层蛋白的LMNA基因突变引起。在C2C12成肌细胞中过表达EDMD核纤层蛋白A的R453W突变会损害肌源性分化。我们在此展示了在C2C12细胞中稳定表达核纤层蛋白A的R453W突变以及邓尼根式部分脂肪营养不良的R482W突变对肌细胞生成素（Myog）基因的转录和表观遗传调控以及对整体染色质组织的影响。R453W - 核纤层蛋白A（而非R482W - 核纤层蛋白A）的表达会损害Myog的激活，并在诱导分化时维持Myog启动子上的抑制性染色质状态，其特征为H3赖氨酸（K）9二甲基化以及H3K4未能超甲基化。表达野生型核纤层蛋白A（WT - LaA）的细胞也无法使H3K4超甲基化。在任何克隆中，Myog启动子DNA甲基化水平均未出现缺陷。在未分化的C2C12细胞中，R453W - 核纤层蛋白A的表达以及程度较轻的R482W - 核纤层蛋白A的表达会使H3K9me3从着丝粒周围异染色质重新分布。R453W - 核纤层蛋白A还会引发H3K27me3从失活的X染色体（Xi）重新分布以及Xi的部分解聚，但维持Xist表达和Xi的覆盖，表明Xi仍处于失活状态。我们的结果表明，基因特异性和全基因组范围的染色质重排可能构成核纤层蛋白病的分子基础。
